The overall objective of this proposal research is to achieve a basic knowledge and understanding of the host-parasite interaction between Culicoides biting midges and selected species of filariae. All phases of the biology, migratory behavior, and maturation of filariae in both singly and multiple-infected culicoid hosts will be carefully followed and described. The filariae chosen for study are the Dipetalonema and Tetrapetalonema species that occur as natural infections in New World primates and local raccoons. Their interaction will be studied in a variety of culicoids such as C. furens, C. hollensis, C. variipennis, and other species as they become available. Through comparative vector studies, efforts will be made to elucidate whether culicoid susceptibility or refractoriness to specific filariae can be attributed to physiological factors. Particular attention will be devoted to the peritrophic membrane as a potential barrier to infection, and to the activity and migratory behavior of ingested microfilariae. By exposing midges to various kinds of food sources, it will be possible to determine the conditions that stimulate peritrophic membrane formation, and to describe its morphology and day-to-day disposition in each culicoid species. Following single and repeated infective blood meals, we hope to ascertain whether this has an effect on the kind or quality of membrane that is formed and whether susceptibility or refractoriness to infection is altered.